Power management applications of interconnect substrates

ABSTRACT

Various applications of interconnect substrates in power management systems are described.

RELATED APPLICATION DATA

The present application is a continuation of and claims priority under35 U.S.C. 120 to U.S. patent application Ser. No. 13/644,693 for PowerManagement Applications of Interconnect Substrates filed on Oct. 4,2012, which claims priority under 35 U.S.C. 119(e) to U.S. ProvisionalPatent Application No. 61/544,945 for Power Management Applications ofPremolded Substrates filed on Oct. 7, 2011, the entire disclosures ofboth of which are incorporated herein by reference for all purposes.

BACKGROUND

The present application relates to the field of interconnect substratesand, more particularly, to the use of interconnect substrates in powermanagement applications.

Semiconductor packaging technology known as Flip-Chip QFN (Quad flat nolead), involves mounting a flip-chip IC on a lead frame comprisingconductive traces etched from a solid sheet of copper. This assembly isthen encased in a molding compound to protect the device from theenvironment. A limitation with this “subtractive” approach to creatingthe conductive traces on which the flip-chip IC is mounted is thatcurrent etching techniques limit the density of the conductive traces.That is, the resolution of copper etching techniques places a lowerbound on the distance between adjacent conductive traces (e.g., about125 microns). This, in turn, limits the pitch of the connections (i.e.,balls, bumps, or pillars) on the device, e.g., a flip-chip IC, to bemounted on the conductive traces. Some improvement can be achieved byreducing the thickness of the copper being etched, but this eventuallyresults in unacceptable reliability issues such as, for example,fragility of the conductive traces and lead frame. Thus, conventionalapproaches to manufacturing conductive traces on a lead frame presentsignificant obstacles to using such techniques with flip-chip and otherpackages having increasing numbers of I/O.

Techniques that employ organic substrates can achieve higher densitiesbut are prohibitively expensive for many applications, and are ofteninferior for more extreme applications, or from a product lifeperspective.

SUMMARY OF THE INVENTION

Interconnect substrates for use in power management applications aredescribed.

According to a particular class of implementations, an interconnectsubstrate is provided for connecting a device to an assembly, the devicebeing characterized by a device pitch and the assembly beingcharacterized by an assembly pitch that is less than about 800 microns.The interconnect substrate includes a plurality of electricallyconductive structures, each of the electrically conductive structuresbeing configured for connection to a corresponding one of a plurality ofcircuit nodes of the device. The electrically conductive structurescorresponding to at least one of the circuit nodes of the device arearranged in an alternating pattern in the interconnect substrate withthe electrically conductive structures corresponding to at least oneother of the circuit nodes. The device pitch is about half the assemblypitch, and a width of at least some of the electrically conductivestructures is at least about two times a spacing between the at leastsome of the electrically conductive structures.

Various of these implementations may include any of the followingfeatures, including any suitable combinations, permutations, or subsetsthereof:

At least some of the circuit nodes of the device correspond to terminalsof one or more power devices; the one or more power devices are part ofa switching regulator; the one or more power devices include two powerdevices, and the terminals include two power node terminals and aswitching terminal; the electrically conductive structures correspondingto the power node terminals and the switching terminal are configuredfor connection to corresponding conductive structures of the assembly.

The interconnect substrate has a first surface for connecting to thedevice and a second surface for connecting to the assembly, and an edge,particular ones of the electrically conductive structures not reachingthe edge of the interconnect substrate; the particular electricallyconductive structures that do not reach the edge of the interconnectsubstrate are configured to connect a corresponding circuit node of thedevice to a corresponding conductive structure of the assembly, at leasta portion of which lies directly under the device; a majority of theelectrically conductive structures of the interconnect substrate liedirectly under the device.

The interconnect substrate has a first surface for connecting to thedevice and a second surface for connecting to the assembly, and an edge,particular ones of the electrically conductive structures extending atleast to the edge of the interconnect substrate.

At least some of the electrically conductive structures have a lengthand a width, and the length is at least four times the width.

At least some of the electrically conductive structures each have one ormore studs thereon configured for connection to a conductive structureof the assembly; the studs are configured to accept solder; the studsinclude plated solder or pre-formed solder; at least some of the studsare circular, and there are multiple circular studs on at least some ofthe electrically conductive structures; at least some of the circularstuds includes solder balls; at least some of the studs includeelongated studs.

The electrically conductive structures corresponding to a first one ofthe circuit nodes of the device extend in a first direction in a primaryplanar orientation of the interconnect substrate, and the electricallyconductive structures corresponding to the first circuit node of thedevice are connected to each other in the interconnect substrate by acommon conductive structure extending in a second direction, the seconddirection not being parallel to the first direction in the primaryplanar orientation of the interconnect substrate; the interconnectsubstrate has a first surface for connecting to the device and a secondsurface for connecting to the assembly, and an edge, and theelectrically conductive structures corresponding to the first circuitnode and the common conductive structure do not reach the edge of theinterconnect substrate; the interconnect substrate has a first surfacefor connecting to the device and a second surface for connecting to theassembly, and an edge, and the common conductive structure is disposednear a portion of the edge of the interconnect substrate therebyallowing for connection of the electrically conductive structurescorresponding to the first circuit node of the device to a singleconductive structure of the assembly; the interconnect substrate has afirst surface for connecting to the device and a second surface forconnecting to the assembly, and an edge, and the common conductivestructure is disposed near a first portion of the edge of theinterconnect substrate, the interconnect substrate further including asecond common conductive structure connecting in the interconnectsubstrate the electrically conductive structures corresponding to asecond one of the circuit nodes of the device, and the second commonconductive structure is disposed near a second portion of the edge ofthe interconnect substrate.

The electrically conductive structures corresponding to two or more ofthe circuit nodes are disposed in a first region of the interconnectsubstrate characterized by a first width-to-spacing ratio of conductivematerial, and the electrically conductive structures corresponding totwo or more others of the circuit nodes are disposed in a second regionof the interconnect substrate characterized by a second width-to-spacingratio of the conductive material that is different from the firstwidth-to-spacing ratio; the device includes at least a portion of aswitching regulator, and the electrically conductive structures disposedin the first region of the interconnect substrate correspond to powerstage nodes of a power stage of the switching regulator, and theelectrically conductive structures disposed in the second region of theinterconnect substrate correspond to control circuit nodes of controlcircuitry of the switching regulator.

The device includes one or more power devices and associated controlcircuitry, and first ones of the electrically conductive structurescorrespond to terminals of the one or more power devices, and secondones of the electrically conductive structures correspond to controlcircuit nodes of the control circuitry; the one or more power devicesand the associated control circuitry are part of a switching regulator.

The interconnect substrate has a first surface for connecting to thedevice, portions of at least some of the electrically conductivestructures being exposed on the first surface of the interconnectsubstrate, the interconnect substrate further including a plurality ofconductive bumps formed on the exposed portions of the electricallyconductive structures and configured for connection with the device; theconductive bumps include any of balls, bumps, pillars, or studs; theconductive bumps include copper pillars formed directly on theelectrically conductive structures; the conductive bumps include copperpillars, and the copper pillars are formed on an under-bumpmetallization (UBM) layer formed on the electrically conductivestructures; the conductive bumps include copper pillars, and the copperpillars reduce the lateral conductivity of the electrically conductivestructures.

The interconnect substrate has a first surface for connecting to thedevice, portions of at least some of the electrically conductivestructures being exposed on the first surface of the interconnectsubstrate and configured for connection to conductive bumps formed onthe device; the conductive bumps include any of balls, bumps, pillars,or studs.

A thermally conductive structure configured for conducting heat from thedevice; at least a portion of the thermally conductive structure extendsthrough the interconnect substrate thereby enabling conduction of theheat from the device to the assembly.

At least some of the electrically conductive structures are configuredfor mounting of discrete passive circuit elements on the interconnectsubstrate.

At least some of the electrically conductive structures includestructural features that promote adhesion with an intervening medium ofthe interconnect substrate, and the structural features include one ormore of wavy edges, jagged edges, zig-zag edges, irregular edges, edgeperforations, or edge protrusions.

The electrically conductive structures arranged in the alternatingpattern include elongated structures corresponding to first and secondcircuit nodes, respectively, the elongated structures being oriented ina first direction in the interconnect substrate, with the elongatedstructures corresponding to the first circuit node alternating with theelongated structures corresponding to the second circuit node; each ofthe electrically conductive structures arranged in the alternatingpattern has a length that is at least four times its width, each of theelectrically conductive structures corresponding to the first circuitnode has one or more studs thereon at an end of the electricallyconductive structure near a first edge of the interconnect substrate,and each of the electrically conductive structures corresponding to thesecond circuit node has one or more studs thereon at an end of theelectrically conductive structure near a second edge of the interconnectsubstrate opposite the first edge, and the studs on the electricallyconductive structures corresponding to the first circuit node areconfigured for connection to a first conductive plane on the assembly,and the studs on the electrically conductive structures corresponding tothe second circuit node are configured for connection to a secondconductive plane on the assembly, the first and second conductive planesbeing adjacent and non-overlapping.

According to another class of implementations, an interconnect substrateis provided for connecting a device to an assembly. The interconnectsubstrate includes a plurality of electrically conductive structures,each of the electrically conductive structures being configured forconnection to a corresponding one of a plurality of circuit nodes of thedevice. One or more of the electrically conductive structurescorresponding to a first circuit node of the device is enclosed in theinterconnect substrate by one or more of the electrically conductivestructures corresponding to a second circuit node of the device.

Various of these implementations may include any of the followingfeatures, including any suitable combinations, permutations, or subsetsthereof:

At least some of the circuit nodes of the device correspond to terminalsof one or more power devices; the one or more power devices are part ofa switching regulator; the one or more power devices include two powerdevices, and the terminals include two power node terminals and aswitching terminal; one of the power node terminals includes the firstcircuit node of the device, and the switching terminal includes thesecond circuit node of the device; the one or more electricallyconductive structures corresponding to the first circuit node, and theone or more of the electrically conductive structures corresponding tothe second circuit node are configured for connection to correspondingconductive structures of the assembly.

The one or more electrically conductive structures corresponding to thefirst circuit node includes a plurality of the electrically conductivestructures, and the one or more electrically conductive structurescorresponding to the second circuit node of the device includes a firstconductive planar structure having a plurality of apertures therein inwhich the electrically conductive structures corresponding to the firstcircuit node of the device are enclosed; the apertures enclosing theelectrically conductive structures corresponding to the first circuitnode form a checkerboard pattern in the first conductive planarstructure; the electrically conductive structures corresponding to thefirst circuit node and the first conductive planar structure areconfigured to connect with the first and second circuit nodes of thedevice, respectively, on one side of the interconnect substrate via aplurality of conductive bumps, and the electrically conductivestructures corresponding to the first circuit node and the firstconductive planar structure are further configured to connect with firstand second assembly conductive planar structures of the assembly,respectively, on an opposing side of the interconnect substrate; thefirst and second assembly conductive planar structures are adjacent andnon-overlapping; the first conductive planar structure is configured toconnect with the second assembly conductive planar structure at an edgeof the first conductive planar structure, and the electricallyconductive structures corresponding to the first circuit node areconfigured to connect to the first assembly conductive planar structureat locations in a direction substantially perpendicular to a primaryplanar orientation of the interconnect substrate; each of a plurality ofthe electrically conductive structures corresponding to a third circuitnode is also enclosed in the interconnect substrate within acorresponding one of the apertures of the first conductive planarstructure.

The device includes at least a portion of a switching regulator, andfirst ones of the electrically conductive structures disposed in a firstregion of the interconnect substrate correspond to power stage nodes ofa power stage of the switching regulator, and second ones of theelectrically conductive structures disposed in a second region of theinterconnect substrate correspond to control circuit nodes of controlcircuitry of the switching regulator.

The interconnect substrate has a first surface for connecting to thedevice, portions of at least some of the electrically conductivestructures being exposed on the first surface of the interconnectsubstrate, the interconnect substrate further including a plurality ofconductive bumps formed on the exposed portions of the electricallyconductive structures and configured for connection with the device; theconductive bumps include any of balls, bumps, pillars, or studs; theconductive bumps include copper pillars formed directly on theelectrically conductive structures; the conductive bumps include copperpillars, and the copper pillars are formed on an under-bumpmetallization (UBM) layer formed on the electrically conductivestructures.

The interconnect substrate has a first surface for connecting to thedevice, portions of at least some of the electrically conductivestructures being exposed on the first surface of the interconnectsubstrate and configured for connection to conductive bumps formed onthe device; the conductive bumps include any of balls, bumps, pillars,or studs.

A thermally conductive structure configured for conducting heat from thedevice; at least a portion of the thermally conductive structure extendsthrough the interconnect substrate thereby enabling conduction of theheat from the device to the assembly.

At least some of the electrically conductive structures are configuredfor mounting of discrete passive circuit elements on the interconnectsubstrate.

At least some of the electrically conductive structures includestructural features that promote adhesion with an intervening medium ofthe interconnect substrate, and the structural features include one ormore of wavy edges, jagged edges, zig-zag edges, irregular edges, edgeperforations, or edge protrusions.

According to another class of implementations, a package is providedthat includes a device including one or more power devices, and aninterconnect substrate for connecting the device to an assembly. Theinterconnect substrate includes a plurality of electrically conductivestructures, first ones of the electrically conductive structurescorresponding to terminals of the one or more power devices. The deviceis mounted on exposed portions of the electrically conductive structuresof the interconnect substrate via conductive bumps.

Various of these implementations may include any of the followingfeatures, including any suitable combinations, permutations, or subsetsthereof:

The one or more power devices are part of a switching regulator.

The one or more power devices include two power devices, and theterminals include two power node terminals and a switching terminal.

At least one of the first electrically conductive structurescorresponding to one of the terminals is enclosed in the interconnectsubstrate by at least one other of the first electrically conductivestructures corresponding to another one of the terminals.

The device includes control circuitry associated with the one or morepower devices, and second ones of the electrically conductive structurescorrespond to control circuit nodes of the control circuitry.

At least some of the electrically conductive structures of theinterconnect substrate have discrete passive circuit elements connectedthereto; the discrete passive circuit elements include a plurality ofcapacitors connected to at least some of the terminals of the one ormore power devices; a first terminal of the one or more power deviceshas two or more of the plurality of capacitors connected thereto, thetwo or more capacitors being mounted on the interconnect substrate alongmore than one edge of the device; the first electrically conductivestructures corresponding to a first terminal of the one or more powerdevices are configured for connection to the assembly along a first edgeof the interconnect substrate, and one or more of the capacitorscorresponding to the first terminal are mounted along a second edge ofthe interconnect substrate different from the first edge; theelectrically conductive structures to which a first one of the discretepassive elements is connected are not configured for connection to theassembly; the first discrete passive circuit element is only accessiblefor testing using a test interface of the device; one or more of thediscrete passive circuit elements are mounted on the interconnectsubstrate between adjacent ones of the conductive bumps; the discretepassive circuit elements include one or more of a capacitor, a resistor,or an inductor.

An underfill material occupying space between the conductive bumpsconnecting the electrically conductive structures of the interconnectsubstrate to the device; the underfill material includes either adispensed underfill or a molded underfill; the underfill material ispart of an encapsulation material at least partially encapsulating thedevice.

The device is mounted on the electrically conductive structures of theinterconnect substrate on a first side of the device, and a second sideof the device opposing the first side is exposed for heat removal; theinterconnect substrate further includes a thermally conductivestructure, the package further including a heat spreader structuremounted on the exposed second side of the device and thermally connectedto the thermally conductive structure of the interconnect substrate topromote heat conduction from the device to the thermally conductivestructure; at least a portion of the thermally conductive structureextends through the interconnect substrate and is configured forconnection to the assembly, thereby enabling conduction of the heat fromthe device to the assembly; one or more portions of a carrier framedisposed along one or more edges of the interconnect substrate adjacentthe device, the heat spreader structure being thermally connected to thethermally conductive structure of the interconnect substrate via theportions of the carrier frame; the carrier frame is rectangular andcontinuous around the device on the interconnect substrate; the carrierframe includes one or more discontinuous segments around the device onthe interconnect substrate; the heat spreader structure includes aplurality of disconnected or partially connected portions, and/or one ormore apertures.

The package of further includes a second device and a secondinterconnect substrate for connecting the second device to the assemblyvia the interconnect substrate, the second interconnect substrateincluding a second plurality of electrically conductive structures, andthe second device is mounted on exposed portions of the second pluralityof electrically conductive structures via second conductive bumps, andthe second interconnect substrate is mounted on the device with at leastsome of the second plurality of electrically conductive structures beingconnected to one or more of the plurality of electrically conductivestructures of the interconnect substrate via third conductive bumpsadjacent an edge of the device; the second device also includes one ormore power devices.

The first electrically conductive structures corresponding to at leastone of the terminals of the one or more power devices are arranged in analternating pattern in the interconnect substrate with the firstelectrically conductive structures corresponding to least one other ofthe terminals of the one or more power devices.

The device is characterized by a device pitch and the assembly ischaracterized by an assembly pitch that is less than about 800 microns,and the device pitch is about half the assembly pitch, and a width of atleast some of the electrically conductive structures is at least about 2times a spacing between the at least some of the electrically conductivestructures.

The interconnect substrate has a first surface connected to the deviceand a second surface connected to the assembly, and an edge, at leastsome of the electrically conductive structures not reaching the edge ofthe interconnect substrate.

The interconnect substrate has a first surface connected to the deviceand a second surface connected to the assembly, and an edge, at leastsome of the electrically conductive structures extending at least to theedge of the interconnect substrate.

At least some of the electrically conductive structures have a lengthand a width, and the length is at least four times the width.

At least some of the electrically conductive structures each have one ormore studs thereon configured for connection to a conductive structureof the assembly; the studs are configured to accept solder; the studsinclude plated solder or pre-formed solder; at least some of the studsare circular, and there are multiple circular studs on at least some ofthe electrically conductive structures; at least some of the circularstuds includes solder balls; at least some of the studs includeelongated studs.

The first electrically conductive structures corresponding to a firstone of the terminals extend in a first direction in a primary planarorientation of the interconnect substrate, and the first electricallyconductive structures corresponding to the first terminal are connectedto each other in the interconnect substrate by a common conductivestructure extending in a second direction, the second direction notbeing parallel to the first direction in the primary planar orientationof the interconnect substrate; the interconnect substrate has a firstsurface for connecting to the device and a second surface for connectingto the assembly, and an edge, and the first electrically conductivestructures corresponding to the first terminal and the common conductivestructure do not reach the edge of the interconnect substrate; theinterconnect substrate has a first surface connected to the device and asecond surface connected to the assembly, and an edge, and the commonconductive structure is disposed near a portion of the edge of theinterconnect substrate and configured for connecting the firstelectrically conductive structures corresponding to the first terminalto a single conductive structure of the assembly; the interconnectsubstrate has a first surface connected to the device and a secondsurface connected to the assembly, and an edge, and the commonconductive structure is disposed near a first portion of the edge of theinterconnect substrate, the interconnect substrate further including asecond common conductive structure connecting in the interconnectsubstrate the first electrically conductive structures corresponding toa second one of the terminals, and the second common conductivestructure is disposed near a second portion of the edge of theinterconnect substrate.

The first electrically conductive structures corresponding to theterminals of the one or more power devices are disposed in a firstregion of the interconnect substrate characterized by a firstwidth-to-spacing ratio of conductive material, and second ones of theelectrically conductive structures corresponding to control circuitnodes of control circuitry associated with the one or more power devicesare disposed in a second region of the interconnect substratecharacterized by a second width-to-spacing ratio of the conductivematerial that is different from the first width-to-spacing ratio.

A thermally conductive structure configured for conducting heat from thedevice; at least a portion of the thermally conductive structure extendsthrough the interconnect substrate and is configured for connection tothe assembly, thereby enabling conduction of the heat from the device tothe assembly.

At least some of the electrically conductive structures includestructural features that promote adhesion with an intervening medium ofthe interconnect substrate, and the structural features include one ormore of wavy edges, jagged edges, zig-zag edges, irregular edges, edgeperforations, or edge protrusions.

At least one of the first electrically conductive structurescorresponding to a first terminal of the one or more power devices isenclosed in the interconnect substrate by one or more of the firstelectrically conductive structures corresponding to a second terminal ofthe one or more power devices; the one or more of the first electricallyconductive structures corresponding to the second terminal includes afirst conductive planar structure having a plurality of aperturestherein in which the first electrically conductive structurescorresponding to the first terminal are enclosed; the aperturesenclosing the first electrically conductive structures corresponding tothe first terminal form a checkerboard pattern in the first conductiveplanar structure; the first electrically conductive structurescorresponding to the first terminal and the first conductive planarstructure are configured to connect with the first and second terminals,respectively, on one side of the interconnect substrate via a subset ofthe conductive bumps, and the first electrically conductive structurescorresponding to the first terminal and the first conductive planarstructure are further configured to connect with first and secondassembly conductive planar structures, respectively, on an opposing sideof the interconnect substrate; at least some of the first electricallyconductive structures include vias that enable current or heatconduction in a direction perpendicular to a primary planar orientationof the interconnect substrate to assembly structures directly under thedevice; the first and second assembly conductive planar structures areadjacent and non-overlapping; the first conductive planar structure isconfigured to connect with the second assembly conductive planarstructure at an edge of the first conductive planar structure, and thefirst electrically conductive structures corresponding to the firstterminal are configured to connect to the first assembly conductiveplanar structure at locations in a direction substantially perpendicularto a primary planar orientation of the interconnect substrate; each of aplurality of the first electrically conductive structures correspondingto a third terminal of the one or more power devices is also enclosed inthe interconnect substrate within a corresponding one of the aperturesof the first conductive planar structure.

The conductive bumps include any of balls, bumps, pillars, or studs; theconductive bumps include copper pillars; the copper pillars are formeddirectly on the electrically conductive structures of the interconnectsubstrate; the copper pillars are formed on an under-bump metallization(UBM) layer formed on the electrically conductive structures of theinterconnect substrate; the device includes a copper redistributionlayer (RDL) and the copper pillars are formed directly on the RDL; thedevice includes a copper redistribution layer (RDL), and the copperpillars are formed on an under-bump metallization (UBM) layer formed onthe RDL.

According to another class of implementations, an interconnect substrateis provided for connecting a device to an assembly, including aplurality of electrically conductive structures. Each of theelectrically conductive structures is configured for connection to acorresponding one of a plurality of circuit nodes of the device. Atleast some of the electrically conductive structures of the interconnectsubstrate have discrete passive circuit elements that are mounted on theinterconnect substrate connected thereto. At least one of theelectrically conductive structures to which a terminal of a first one ofthe discrete passive elements is connected is configured only forconnection to the device and not to the assembly.

Various of these implementations may include any of the followingfeatures, including any suitable combinations, permutations, or subsetsthereof

Two or more of the discrete passive circuit elements are configured forconnection to a first circuit node of the device, the two or morediscrete passive circuit elements being mounted along more than one edgeof the interconnect substrate.

The electrically conductive structures corresponding to a first circuitnode of the device are configured for connection to the assembly along afirst edge of the interconnect substrate, and one or more of thediscrete passive circuit elements corresponding to the first circuitnode are mounted on a second edge of the interconnect substratedifferent from the first edge.

One or more of the discrete passive circuit elements are mounted on theinterconnect substrate at locations between exposed portions of theelectrically conductive structures of the interconnect substrateconfigured for connection to the device.

The discrete passive circuit elements include one or more of acapacitor, a resistor, or an inductor.

The device includes one or more power devices, at least some of theelectrically conductive structures corresponding to terminals of the oneor more power devices, and the discrete passive circuit elements includea plurality of capacitors configured for connection to at least some ofthe terminals of the one or more power devices.

The first discrete passive circuit element and the correspondingelectrically conductive structures are configured such that, when thedevice, the interconnect substrate and the assembly are connected, thefirst discrete passive circuit element is only accessible for testingusing a test interface of the device.

According to another class of implementations, an interconnect substrateis provided for connecting a device to an assembly, including aplurality of electrically conductive structures. Each of theelectrically conductive structures is configured for connection to acorresponding one of a plurality of circuit nodes of the device. Atleast some of the electrically conductive structures of the interconnectsubstrate have discrete passive circuit elements that are mounted on theinterconnect substrate connected thereto. Two or more of the discretepassive circuit elements are configured for connection to a firstcircuit node of the device. The two or more discrete passive circuitelements are mounted along more than one of edge of the interconnectsubstrate.

Various of these implementations may include any of the followingfeatures, including any suitable combinations, permutations, or subsetsthereof:

The electrically conductive structures corresponding to the firstcircuit node of the device are configured for connection to the assemblyalong a first edge of the interconnect substrate, the first edge beingdifferent than at least one of the edges along which the two or morediscrete passive circuit elements are mounted.

One or more of the discrete passive circuit elements are mounted on theinterconnect substrate at locations between exposed portions of theelectrically conductive structures of the interconnect substrateconfigured for connection to the device.

The discrete passive circuit elements include one or more of acapacitor, a resistor, or an inductor.

The device includes one or more power devices, at least some of theelectrically conductive structures corresponding to terminals of the oneor more power devices, and the discrete passive circuit elements includea plurality of capacitors configured for connection to at least some ofthe terminals of the one or more power devices.

According to another class of implementations, an interconnect substrateis provided for connecting a device to an assembly, including aplurality of electrically conductive structures. Each of theelectrically conductive structures is configured for connection to acorresponding one of a plurality of circuit nodes of the device. Atleast some of the electrically conductive structures of the interconnectsubstrate have discrete passive circuit elements that are mounted on theinterconnect substrate connected thereto. The electrically conductivestructures corresponding to a first circuit node of the device areconfigured for connection to the assembly along a first edge of theinterconnect substrate, and one or more of the discrete passive circuitelements corresponding to the first circuit node are mounted on a secondedge of the interconnect substrate different from the first edge.

Various of these implementations may include any of the followingfeatures, including any suitable combinations, permutations, or subsetsthereof:

Two or more of the discrete passive circuit elements are configured forconnection to the first circuit node of the device, the two or morediscrete passive circuit elements being mounted along more than one edgeof the interconnect substrate.

One or more of the discrete passive circuit elements are mounted on theinterconnect substrate at locations between exposed portions of theelectrically conductive structures of the interconnect substrateconfigured for connection to the device.

The discrete passive circuit elements include one or more of acapacitor, a resistor, or an inductor.

The device includes one or more power devices, at least some of theelectrically conductive structures corresponding to terminals of the oneor more power devices, and the discrete passive circuit elements includea plurality of capacitors configured for connection to at least some ofthe terminals of the one or more power devices.

According to another class of implementations, a bumped device isprovided that includes a plurality of conductive structures including aredistribution layer (RDL), and a plurality of copper pillars formeddirectly on the RDL without passivating material between the copperpillars and the RDL.

Various of these implementations may include any of the followingfeatures, including any suitable combinations, permutations, or subsetsthereof:

A passivating layer covering the RDL through which the copper pillarsextend.

The copper pillars reduce the lateral conductivity of the electricallyconductive structures.

The device includes an integrated circuit.

The bumped device includes one or more power devices having a pluralityof terminals; the one or more power devices are part of a switchingregulator; the one or more power devices include two power devices, andthe terminals include two power node terminals and a switching terminal;the copper pillars are configured to connect the terminals of the one ormore power devices to electrically conductive structures of a substrate.

According to another class of implementations, a method for fabricatinga device is provided. A seed layer is sputtered over an accessiblemetallization of an underlying substrate. A first photoresist layerhaving a first pattern is placed over the seed layer. A first conductivemetal layer is plated using the seed layer according to the firstpattern. A second photoresist having a second pattern is placed over thefirst conductive metal layer. A second conductive metal layer is platedusing the seed layer according to the second pattern. The secondconductive metal layer is formed without passivating material betweenthe second conductive metal layer and the first conductive metal layer.The seed layer is etched.

Various of these implementations may include any of the followingfeatures, including any suitable combinations, permutations, or subsetsthereof:

The first and second conductive metal layers include copper.

The first conductive metal layer includes a copper redistribution layer(RDL) and the second conductive metal layer includes a plurality ofcopper pillars; a passivating material is deposited over the RDL andcopper pillars; solder is plated on the copper pillars.

One or more additional conductive metal layers are plated using the seedlayer.

The first photoresist layer is stripped before applying the secondphotoresist layer.

The first and second photoresist layers are stripped substantiallysimultaneously.

According to another class of implementations, an interconnect substrateis provided for connecting a device to an assembly. The device includesa power stage of a switching regulator. The power stage has first andsecond power node terminals and a switching terminal. The interconnectsubstrate includes a plurality of electrically conductive structures,first ones of the electrically conductive structures being configuredfor connection to the first power node terminal, second ones of theelectrically conductive structures being configured for connection tothe switching terminal, and third ones of the electrically conductivestructures being configured for connection to the second power nodeterminal. The first, second, and third electrically conductivestructures are arranged in the interconnect substrate such that currentin the second electrically conductive structures resulting fromoperation of the power stage of the switching regulator remainssubstantially constant when conduction is commutated between the firstelectrically conductive structures and the third electrically conductivestructures.

Various of these implementations may include any of the followingfeatures, including any suitable combinations, permutations, or subsetsthereof:

Each of the second electrically conductive structures is adjacent one ofthe first electrically conductive structures and one of the thirdelectrically conductive structures; each of the second electricallyconductive structures has one of the first electrically conductivestructures on a first side of the second electrically conductivestructure and one of the third electrically conductive structures on anopposing side of the second electrically conductive structure oppositethe first side.

According to another class of implementations, a package is provide thatincludes, including a device including a power stage of a switchingvoltage regulator, the power stage having first and second power nodeterminals and a switching terminal. The package also includes aninterconnect substrate for connecting the device to an assembly. Theinterconnect substrate includes a plurality of electrically conductivestructures, first ones of the electrically conductive structures beingconnected to the first power node terminal, second ones of theelectrically conductive structures being connected to the switchingterminal, and third ones of the electrically conductive structures beingconnected to the second power node terminal. The first, second, andthird electrically conductive structures are arranged in theinterconnect substrate such that current in the second electricallyconductive structures resulting from operation of the power stage of theswitching regulator remains substantially constant when conduction iscommutated between the first electrically conductive structures and thethird electrically conductive structures.

Various of these implementations may include any of the followingfeatures, including any suitable combinations, permutations, or subsetsthereof:

Each of the second electrically conductive structures is adjacent one ofthe first electrically conductive structures and one of the thirdelectrically conductive structures; each of the second electricallyconductive structures has one of the first electrically conductivestructures on a first side of the second electrically conductivestructure and one of the third electrically conductive structures on anopposing side of the second electrically conductive structure oppositethe first side.

According to another class of implementations, a bumped device isprovides that includes a power stage of a switching voltage regulator,the power stage having first and second power node terminals and aswitching terminal. The bumped device also includes a plurality ofconductive bumps arranged on a surface thereof and configured forfacilitating external connections to the first and second power nodeterminals and the switching terminal of the power stage of the switchingvoltage regulator. First ones of the conductive bumps are electricallyconnected to the first power node terminal, second ones of theconductive bumps are electrically connected to the switching terminal,and third ones of the conductive bumps are electrically connected to thesecond power node terminal. The power stage of the switching regulatoris configured and the first, second, and third conductive bumps arearranged such that current in the second conductive bumps resulting fromoperation of the power stage of the switching regulator remainssubstantially constant when conduction is commutated between the firstconductive bumps and the third conductive bumps.

Various of these implementations may include any of the followingfeatures, including any suitable combinations, permutations, or subsetsthereof:

Each of a plurality of subsets of the second conductive bumps isadjacent one of a plurality of subsets of the first conductive bumps andone of a plurality of subsets of the third conductive bumps; each of theplurality of subsets of the first, second, and third conductive bumps isarranged in a row, each row of the second conductive bumps having a rowof the first conductive bumps on a first side of the row of secondconductive bumps, and a row of the third conductive bumps on an opposingside of the row of the second conductive bumps opposite the first side.

The conductive bumps include any of balls, bumps, pillars, or studs.

The conductive bumps include copper pillars; the bumped device includesa copper redistribution layer (RDL) and the copper pillars are formeddirectly on the RDL; the bumped device includes a copper redistributionlayer (RDL), and the copper pillars are formed on an under-bumpmetallization (UBM) layer formed on the RDL.

The conductive bumps are elongated.

A further understanding of the nature and advantages of the presentinvention may be realized by reference to the remaining portions of thespecification and the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a particular implementation of an interconnectsubstrate.

FIG. 2 illustrates another implementation of an interconnect substrate.

FIG. 3 illustrates another implementation of an interconnect substrate.

FIG. 4 illustrates a pattern of conductive bumps that may be employedwith a particular implementation of an interconnect substrate.

FIGS. 5(a)-5(e) illustrate various components of a particularimplementation of an interconnect substrate and a corresponding patternof conductive bumps.

FIGS. 6(a) and 6(b) illustrate further implementations of interconnectsubstrates and corresponding devices mounted thereon.

FIGS. 7 and 8 illustrate implementations of interconnect substrates withdevices and heat spreaders mounted thereon.

FIG. 9 illustrates stacked interconnect substrates and devices.

FIGS. 10(a)-10(c) illustrate various aspects of a particularimplementation of an interconnect substrate with passive componentsmounted thereon.

FIG. 11 illustrates various implementations of conductive elements inparticular implementations of interconnect substrates.

FIGS. 12 and 13(a)-13(c) illustrate conductive structures that may beemployed with various implementations.

FIGS. 14 and 15 illustrate particular arrangements of conductiveelements of particular implementations of interconnect substrates.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

Reference will now be made in detail to specific embodiments of theinvention including the best modes contemplated by the inventors forcarrying out the invention. Examples of these specific embodiments areillustrated in the accompanying drawings. While the invention isdescribed in conjunction with these specific embodiments, it will beunderstood that it is not intended to limit the invention to thedescribed embodiments. On the contrary, it is intended to coveralternatives, modifications, and equivalents as may be included withinthe spirit and scope of the invention as defined by the appended claims.In the following description, specific details are set forth in order toprovide a thorough understanding of the present invention. The presentinvention may be practiced without some or all of these specificdetails. In addition, well known features may not have been described indetail to avoid unnecessarily obscuring the invention.

Semiconductor packaging technology known as Flip-Chip QFN (Quad flat nolead), involves mounting a flip-chip IC on a lead frame comprisingconductive traces etched from a solid sheet of copper. This assembly isthen encased in a molding compound to protect the device from theenvironment. A limitation with this “subtractive” approach to creatingthe conductive traces on which the flip-chip IC is mounted is thatcurrent etching techniques limit the density of the conductive traces.That is, the resolution of copper etching techniques places a lowerbound on the distance between adjacent conductive traces (e.g., about125 microns). This, in turn, limits the pitch of the connections (i.e.,balls, bumps, or pillars) on the device, e.g., a flip-chip IC, to bemounted on the conductive traces. Some improvement can be achieved byreducing the thickness of the copper being etched, but this eventuallyresults in unacceptable reliability issues such as, for example,fragility of the conductive traces and lead frame. Thus, conventionalapproaches to manufacturing conductive traces on a lead frame presentsignificant obstacles to using such techniques with flip-chip and otherpackages having increasing numbers of I/O.

Techniques that employ organic substrates can achieve higher densitiesbut are prohibitively expensive for many applications, and are ofteninferior for more extreme applications, or from a product lifeperspective.

Premolded substrates in which conductive traces are manufactured using“additive” techniques (e.g., plating up the conductive traces on asubstrate) may achieve suitably high densities in some applications(e.g., about 40-50 microns between conductive traces and potentially aslow as 30 microns in some cases).

Various premolded substrates described herein may be characterized by afirst set of benefits derived from advantages of plating technologyrelative to etching technology, and/or a second set of benefits derivedfrom advantages of premolded structures relative to conventional leadframes.

With regard to plating vs. etching, etched traces have limitationsrelative to plated traces in terms of the trace aspect ratio that isachievable. For example, when etching from two sides of a sheet ofcopper, conventional processes can typically only achieve a spacingbetween traces of slightly more than half the thickness of the traces.By contrast, plating is regularly seen to produce much higher aspectratio structures. There are ways to achieve similar spacing usingetching but they require etching only a thin layer. Thus, one advantageof plating relative to etching is higher aspect ratio structures (e.g.,110 um trace thickness with 40 um spacing between traces).

In addition, premolded substrates (which can be created with bothetching and plating techniques) have an advantage relative toconventional lead frames in that an actual frame for the conductivetraces is not required for premolded substrates. That is, withconventional lead frames, the intermediate etched traces must beconnected to a frame that keeps the structure together until molding.This imposes the requirement that all traces reach to the edge of thedevice, i.e., no floating structures internal to the device can becreated. This makes it difficult to create area array and multi-rowpackages as there is no way to have internal floating conductivestructures that do not reach the edge of the device. Because premoldedsubstrates do not require such a frame, they are not limited in thisway.

As will become apparent with reference to the description of specificembodiments below, a variety of advantages may be achieved withpremolded substrates implemented as described herein. For example, aconventional lead frame fabricated using etching with 200 um thicknesstypically yields conductive traces that are 250 um wide with a 400 umpitch. By comparison and in accordance with one or more embodimentsdescribed herein, for the same conductive trace width, a 290 um pitchmay be achieved in premolded substrates using plating; a reduction of110 um. If one were to attempt to reduce the width of the conductivetraces of a conventional lead frame below 250 um, the etching processwould result in structures that are not mechanically stable. Forexample, if such structures are created in half etch, they would formcantilever bridges that are limited with respect to how far they canextend. While trace width in etched lead frames can theoretically bereduced to 125 um (thereby achieving a 275 um pitch with 150 umspacing), such structures are severely restricted in length. Bycomparison, the conductive traces of a premolded substrate are supportedby the molding compound in which they are suspended and can travel greatdistances, e.g., more than 4× their width.

In addition, while the pitch on some devices (e.g., flip-chip devices)can be very low (e.g., 150 um), the pitch on printed circuit boards(PCBs) is generally 500 um (with limited applications having a 400 umpitch). In general, the current state of the art for PCB and viatechnology does not permit the reduction of pitch below 500 um without aprohibitive increase in cost (for most applications). This is due to thefact that PCBs are typically manufactured using etching technologies(with some additive plating for vias and outer layers). Thus, because ofthis limitation of PCBs, external device pitch needs to remain at 500 umwhile internal device pitch needs to be fanned in to any reduced pitch.Unfortunately, conventional lead frame technology puts practical limitson internal device pitch that cannot effectively match the very lowpitches and high I/O counts by which some device technologies, e.g.,flip-chip devices, are characterized. Various embodiments are describedbelow which illustrate one or more of the advantages of premoldedsubstrates with respect to these design issues.

According to some embodiments, premolded substrates may be manufacturedas follows. A carrier substrate or carrier frame (e.g., steel may beused as a low cost option) is pre-plated with a thin film of copper topromote plating. The conductive traces (including a second layer ofconducive traces on top of the first layer of conductive traces (namelystuds) are plated on the copper and then a molding material is depositedover the conductive traces and the carrier. The molding material is thenground away to expose the studs for connection of the premoldedsubstrate to another assembly, e.g., a printed circuit board (PCB). Incontrast with conventional subtractive techniques for lead frameformation, the additive process with which these conductive traces areformed allows flexibility in where the pads may be placed. The carrieris then etched away from the other side of the assembly to expose theconductive traces embedded in the molding material. An insulating layeris optionally deposited over the conductive traces in which pads maythen be formed where the bumped device to be mounted on the premoldedsubstrate will make contact with the premolded substrate conductivetraces. For more information regarding premolded substrate techniquesthat may be employed with various embodiments of the invention, pleaserefer to U.S. Patent Publication No. 2008/0145967 for SemiconductorPackage and Manufacturing Method Thereof published on Jun. 19, 2008, theentire disclosure of which is incorporated herein by reference for allpurposes.

Various embodiments of the inventions described herein relate to the useof interconnect substrates, e.g., premolded substrates, for interfacingwith bumped semiconductor packages, e.g., flip chips, and, morespecifically, bumped semiconductor packages used in power managementapplications. As used herein, “bumped device” refers to anysemiconductor device having an array of conductive elements (e.g.,balls, bumps, pillars, etc.) arranged across a surface of the device formaking electrical connections to other devices, boards, assemblies, orsubstrates.

FIG. 1 shows conductive traces in a premolded substrate configured forconnecting with an overlying bumped device and also with the controlpads and conductive planes on an underlying PCB. According to aparticular class of embodiments, the conductive planes represent, forexample, the three terminals of a switching voltage regulator, two ofwhich are shown in FIG. 1, i.e., the VX plane and the Ground/VSS plane.As shown, the conductive traces that connect to the underlyingconductive planes resemble fingers that alternate or are“interdigitated.” The circular studs exposing the conductive traces arealigned with the corresponding conductive plane on the underlying PCB.Connection between the studs and the conductive planes may be made usingany suitable technology, e.g., balls, bumps, pillars, paste, etc.

FIG. 2 shows conductive traces in another premolded substrate alsoconfigured for connecting with an overlying bumped device and also withthe control pads and conductive planes on an underlying PCB. Again, inthis example, the conductive planes represent the three terminals of aswitching voltage regulator. However, in contrast with FIG. 1, the studsare formed along the length of the conductive traces and form leadfingers for connecting with the underlying PCB. In addition, theconductive traces of FIG. 2 that correspond to the same conductive planeon the PCB are electrically connected to each other (via a horizontalbus) in contrast with the isolation between adjacent conductive tracesshown in FIG. 1. The electrically connected conductive traces with theequivalent exposed stud after back grinding the mold compound are moreclearly represented in FIG. 3.

The upper portion of FIG. 3 shows the interconnected VX conductivetraces, the interconnected VSS conductive traces, and the interconnectedVDD conductive traces suspended in the premolded substrate, each set ofconductive traces corresponding to a conductive plane on the PCB towhich it will be connected. The horizontal bus which interconnects thevertical fingers of each set of conductive traces may be advantageousfor some implementations, allowing a single terminal connection to theinterconnected conductive traces. Such an approach may also beadvantageous in that electrical connectivity may be better ensured inthe event of individual lead or connection failure.

The lower portion of FIG. 3 shows the pattern of studs (in the form oflead fingers) formed on the conductive traces that will make the directconnection to the conductive planes and pads on the underlying PCB. Itshould be noted that the use of balls, bumps, or pillars instead ofleads may result in improvements in board level reliability. Someembodiments are discussed below. It should also be understood that allof these structures (balls, bumps, pillars, studs, etc.) may be formedon isolated conductive traces as well such as those shown, for example,in FIG. 1. FIG. 4 shows an IC pad and pin out layout pattern of balls,bumps, or pillars that may be formed on the conductive traces of thestructure shown in the upper portion of FIG. 3 (with VSS being labeledas GND in this example). This pattern of balls, bumps, or pillars may beformed on the premolded substrate conductive traces, IC device or both.

One advantage associated with some of these embodiments is the abilityto improve I/O density while maintaining a similar footprint to currentdesigns employing more conventional approaches, e.g., QFN, BGA, TSOP,J-lead, Gull-Wing, etc. Improved I/O density in the context of powermanagement integrated circuits allows designers more flexibility in thecontrol and monitoring of such devices and, in particular, the abilityto include I/O to the outside world in the same device as the switchingcircuitry as opposed to separate control ICs. In addition, the pitchbetween high current conductive traces (e.g., VX, VSS, and VDD traces)may be reduced with corresponding reductions in resistance and alsoswitching losses). Improvements relating to electromigration may also berealized in that the increased density means that there is more solderper unit area. More uniform distribution of power from increased densitymay also result in better thermal performance.

And it should be appreciated that the conductive trace patterns andconnective structures described are merely examples illustrating themany potential configurations and applications of premolded substratesin the context of power management devices and systems. Another exampleof a configuration in which the balls, bumps, or pillars on the tracesare themselves “interdigitated” is shown in FIG. 5(a). As shown, islandsare formed in the VX conductive plane for the balls, bumps, or pillarsconnecting to VDD and VSS/GND. The illustrated pattern is intended toreduce internal metal connection resistance in order to improve total onstate resistance (Rdson) of the switching semiconductor element. Thisapproach is also intended to improve PCB connections with the use ofsolid conduction planes to reduce PCB resistance and improve thermalconductivity. It may also facilitate assembly for PCB mounting due tolarger solder pad connections. For more information on techniques forinterdigitating conductive traces and/or configurations of balls, bumps,or pillars for use with embodiments of the invention, please refer toU.S. patent application Ser. No. 12/344,134 for Lead Assembly for aFlip-Chip Power Switch filed Dec. 24, 2008, the entire disclosure ofwhich is incorporated herein by reference for all purposes.

FIGS. 5(b)-5(e) show additional detail of copper pillar bumps andon-chip metal connections for a configuration of interdigitated nodessuch as that shown in FIG. 5(a). An exploded perspective view of thedetail Area A of FIG. 5(b) is shown in FIG. 5(c) and illustrates theon-chip metal connections for the nodes in Area A. An explodedperspective view of the detail Area B of FIG. 5(b) is shown in FIG. 5(d)and illustrates the on-chip metal connections for the nodes in Area B.An exploded perspective view of the detail Area C of FIG. 5(b) is shownin FIG. 5(e) and illustrates the on-chip metal connections for the nodesin Area C. As shown in each of FIGS. 5(c)-5(e), all of the layersbetween metal layer 3 (M3) and the under bump metal (UBM) having thesame electrical polarity and corresponding to the same regulatorterminal are connected through inter-stitches.

The interdigitated configuration of the conductive traces in some of theembodiments discussed herein (e.g., FIGS. 1-3) results in an externaldevice pitch at 2X the pitch of internal traces, i.e., because onlyevery other trace is connected to the same conductive element on theunderlying PCB. It follows then that internal device pitch can bereduced to 250 um without pushing the external device pitch of the PCBbelow its typical limit of 500 um. In a premolded substrate constructedin accordance with embodiments of the invention and having a 40 umspacing between conductive traces, this results in a trace width of 210um. By contrast, conventional lead frame technology would require atrace width of 100 um; well below the recommended limit for a robuststructure. In addition to being fragile, such a trace width would likelybe inadequate for current flow, and result in an unacceptably smalldevice pad width (e.g., 100 um); far below the currently acceptablesolderable width for conventional lead frame technology.

According to some embodiments, a premolded substrate facilitates notonly the fan-in of the I/O sections of the internal device, but alsoenables the creation of an area array in the I/O section, thus allowingan increase in I/O density compared to peripheral devices such asconventional lead frames. It should be noted that such embodiments canalso be realized using LGA or BGA variants of the premolded substrateconnectivity to the printed circuit board.

According to some embodiments, the co-location of common traces on oneside of the device allows the PCB pitch rules to be relaxed in that allof the traces on the same side (e.g., VX or VSS) can be contacted to asolid conductive plane thus removing the need for fine etching andtraces on the PCB for this purpose allowing further reduction of pitchbelow 500 um in the future. Furthermore, such designs need not placevias in the PCB pads; an approach that causes issues during reflow assuch vias trap solder voids and reduce board level reliability. That is,embodiments are contemplated that allow vias in the VX, VSS and VDDplanes to be located between solder openings in the solder mask that areconfigured to connect to the conductive traces, traces of solderableareas of the LGA, and/or solder balls of the BGA variants of thepremolded substrates. The vias allow connection of multiple layers inthe PCB directly underneath the device. Such an approach cansignificantly increase via density relative to conventional lead framedesigns, thereby enabling lower electrical loss as well as betterthermal conductivity from the device package to the board.

Examples of classes of power management devices and systems that mayemploy suitably configured premolded substrates as described hereininclude, for example, those described in and covered by the claims ofU.S. Pat. No. 6,278,264 for Flip-Chip Switching Regulator issued on Aug.21, 2001, the entire disclosure of which is incorporated herein byreference for all purposes. A wide variety of other power managementdevices and systems, and other bumped devices that may benefit fromspecific embodiments described herein will also be apparent to those ofskill in the art.

According to a particular class of embodiments, the backside of thebumped device that is mounted on the conductive traces of the premoldedsubstrate may be exposed. That is, once the bumped device is mounted onthe premolded substrate, the combined structure can be molded on allsides except the backside of the bumped device, or it can be overmoldedon all sides with a portion of the overmolding being subsequentlyremoved (e.g., by etching or grinding) to expose the backside of thebumped device.

FIG. 6(a) shows a premolded substrate similar to the one shown in FIG. 1as well as two alternative cross-sections of the premolded substratewith a mounted bumped device. In the examples shown, the backside of thebumped device (a) is shown exposed. The bumped device is shown connectedto the conductive traces (d) of the premolded substrate via copperpillars (b) and solder bumps (c) although a variety of other types ofconnections can be employed. The studs (e) along the conductive tracesalso have solder (in the form of solder balls (f) in this example) formaking the connection to the PCB (not shown).

And as shown in FIG. 6(a) (lower device cross-section), embodiments ofthe invention may employ conventional underfill to fill in the spacesbetween the connections to the bumped device. That is, once the bumpeddevice is attached and before an overmolding is applied, an underfillmaterial is dispensed which flows underneath the device and fills theinterstices under the device by a capillary action. The underfillmaterial may be any suitable conventional underfill material and is wellsuited for implementations having high I/O density with an extremelyfine pitch.

Alternatively, embodiments are contemplated in which a molded underfillmay be employed (upper device cross-section in FIG. 6(a)). Moldedunderfill replaces the dispensed underfill with a molding material whichis introduced using a molding-type process. The coarser materialsincluded in the molding compound make the process more challenging thandispensing conventional underfill (particularly for extremely fine pitchapplications), but the materials are considerably less expensive. Moldedunderfill may also contribute to improved reliability in that it mayprovide more robust mechanical and/or environmental protection thanconventional underfill materials. FIG. 6(b) shows another premoldedsubstrate similar to the upper device cross-section of FIG. 6(a), but inwhich the balls, bumps, or pillars on the traces are interdigitated in amanner similar to that shown in FIG. 5(a).

According to a class of embodiments illustrated in FIGS. 7 and 8, heatspreader structures are connected to the exposed backside of the mountedbumped device to provide thermally conductive pathways for removal ofheat from the bumped device. FIG. 7 illustrates three heat spreaderconfigurations that provide thermal conduction in two dimensions, i.e.,up through the heat spreader, and laterally to the portions of the heatspreader that extend beyond underlying semiconductor device. Integratedheat spreader extensions can be used as thermal and/or electricalconnections. As shown in the middle illustration of FIG. 7, the heatspreader can be brought down into contact with the PCB to promoteadditional heat transfer via the PCB through convection. As shown in thebottom illustration of FIG. 7, integrated heat spreader extensions canalso be attached to the premolded substrate conductive traces and/or tothe PCB via studs and solder joints. Such embodiments may beparticularly important as the power per unit die area and I/O densitycontinue to increase.

According to a particular class of embodiments illustrated in FIG. 8, atleast a portion of the carrier substrate (i.e., the carrier frame) ismaintained around the edges of the window etched away to expose theconductive traces suspended in the premolded substrate. The frame may berectangular and continuous around the device, or in one or morediscontinuous segments around the edge, e.g., at the four corners of theassembly, along one or more edges, etc. This carrier frame providesadditional thermal path(s) to the PCB for improved thermal performance.The upper two diagrams show embodiments in which the heat spreaderextends beyond the carrier frame in a manner similar to the embodimentsshown in FIG. 7. It should be noted that these heat spreader extensionsmay also be connected to the premolded substrate conductive tracesand/or to the PCB as shown in the bottom diagram of FIG. 7. The bottomdiagram shows an embodiment in which the heat spreader does not extendbeyond the carrier frame, and the primary thermal path to the PCB istherefore via the carrier frame. In the depicted example, the carrierframe is shown connected to the PCB ground plane. Also contemplated areheat spreader structures having multiple disconnected or partiallyconnected portions, and/or one or more apertures. Such structures mayreduce stresses that might otherwise result from thermal expansion ormechanical strain acting on a device having a continuous heat spreader.

Heat spreader structures which may be used with various embodiments ofthe invention are described in U.S. patent application Ser. No.12/716,197 for Chip-Scale Packaging with Protective Heat Spreader filedMar. 2, 2010, the entire disclosure of which is incorporated herein byreference for all purposes.

Embodiments are contemplated in which multiple premolded substratesenable the stacking of bumped devices and/or other active or passivecomponents as shown in FIG. 9. The top diagram shows two premoldedsubstrates stacked with two bumped devices (with underfill), in whichelectrical connections between the two devices are made around the edgeof the lower device in the stack (solder balls are shown, but anysuitable structure can be used). The middle diagram shows the additionof a passive component (e.g., capacitor, resistor, inductor, etc.). Thebottom diagram shows the use of molded underfill as discussed above. Thedepicted uses of conventional or molded underfill are merely examples.Embodiments are also contemplated in which one premoldedsubstrate/bumped device assembly could use conventional underfill whileanother uses molded underfill. It should also be understood thatstacking is not limited to two assemblies, i.e., that an arbitrarynumber of devices and premolded substrates may be stacked as describedherein as appropriate for particular applications.

FIGS. 10(a)-10(c) show different views of an embodiment in which passivecomponents, in this case decoupling capacitors (components 0201), areprovided on both edges of the die (connected between the hatchedrectangular pads) even though external pads for VDDH and VCC are onlyprovided along one edge of the die. FIG. 10(a) shows the orientation ofthe bumps (e.g., 1002) on the overlying die 1004 to the conductivetraces of the premolded substrate. FIG. 10(b) shows the pattern ofballs, bumps or pillars (e.g., 1022) on the conductive traces of thepremolded substrate for connecting to the underlying PCB. FIG. 10(c)shows the orientation of the VX, VDDH, and VSS/GND conductive regions ofthe underlying PCB to the balls, bumps or pillars (e.g., 1022) on theconductive traces of the premolded substrate to which the conductiveplanes connect, as well as the vias to internal layers of the PCB.

The advantage of having the VDDH to VCC (or Analog VDD) capacitors onboth edges of the die is that effective high frequency decoupling islimited by the stray inductance in connecting the capacitor to the diein question. Stray inductance switching loss is important in lieu of thehigh current requirement chips as it contributes LI^2f switching losswhich at 1 Mhz switching frequency makes 1 nH equivalent to 1 mOhm loss.Having two capacitors on two edges of the die cuts the stray inductancein half compared to a capacitor on one edge of the die. One couldachieve the same by placing external pads for VDDH and VCC on both edgesof the package but that would restrict the location for routing theswitching node of the regulator out of the die. In this way, while thedecoupling is provided on both edges of the die using internal routing,the external routing is limited to having VDDH and VCC on one edge ofthe package and having switching node VX on the other edge of thepackage. Furthermore, one can also co-locate the boot strap (BST) anddriver decoupling capacitors on the same edges as the high frequencydecoupling capacitors. Integrating these capacitors inside the packagecan potentially remove the need for having the I/O for these connectionsoutside of the package (apart from the need to have them accessible forautomated test). As such, the routing of VCC-driver supply andVBST-boost supply can be provided on internal I/O that do not have therequirement to be routable on the PCB but only accessible duringautomated test. Integrating any kind of capacitor is advantageous evenif they are only on one side of the die as the stray inductance to thatcapacitor is reduced relative to a PCB mounted capacitor that would bephysically further away (by the thickness of a conventional lead frame)than with the shown structure. Embodiments of the premolded substratesdescribed herein allow the integration of capacitors on both sides ofthe die due to flexibility in their internal routing. These premoldedsubstrates offer benefits relative to conventional lead frames as thestandoff of the finer pitch die from the conductive traces/leads can belower and the capacitors can be smaller thus allowing lower inductanceconnections for capacitors bypassing the devices. Finally, inductance issomewhat defined by the distance that current travels in closing theloop and the distance between the return paths in that loop. Pre-platedtraces with 30-40 um pitch additionally add to the reduction of strayinductance between the die and the capacitors as the high frequencycurrents will travel the closest possible path (i.e., the surface of theconductors) and thus the spacing of the conductors will inevitablydefine the stray inductance of the connections. And while the integratedpassive components are shown at the edge of the devices, it should beunderstood that embodiments are contemplated in which passive componentsmay be integrated in such structures between pillars (e.g., between thepillars shown in any of the structures depicted in FIGS. 6(a)-9) tofurther reduce inductance.

While only the capacitors are shown as integrated one could integratepassive components such as resistors into the same package and thuscreate accurate references for the chip more easily than using on-dieresistors. Such off-die resistors can have controlled temperaturecoefficients, yet their temperature can be closely related to the dietemperature as they are co-packaged close to the die. Again theseinternal resistors could be only accessible during ATE test or notaccessible whatsoever from ATE but only through the die-ATE testinterface.

As the distance between conductive traces in the premolded substratebecomes smaller, adhesion between the metal (e.g., copper) of the tracesand the molding compound in which the traces are suspended may become areliability issue. Therefore, embodiments are contemplated in which thisadhesion is improved or optimized by controlling the thicknesses of thetraces, the widths of the traces, and/or the distance between traces inrelation to one another. In addition, and according to some embodiments,a variety of structural features may be introduced in the traces andstuds to promote adhesion. Examples of such structural features areshown in FIG. 11. In the left-hand diagram both the traces and the studsfor connecting the premolded apparatus to the PCB are wavy to increasethe amount of surface area at which the different materials interface.In the right-hand diagram wavy traces are combined with straight studs.A wide variety of other traces variations (e.g., jagged, zig-zag,irregular, edge perforations, edge protrusions, etc.) may be suitablefor various implementations. Another advantage of some structuralfeatures is that they may act to inhibit cracks in the molding materialfrom propagating along the material. That is, the structural features ofthe conductive traces and studs may provide termination points that actas “crack arrests.”

According to a particular class of embodiments, the external connectionson a bumped device (e.g., a flip-chip to be mounted on the conductivetraces in a premolded substrate) are copper pillar structures as shownin FIGS. 12 and 13(a)-13(c). It should be noted that such structures mayalso be formed on the conductive traces of the premolded substrate.Conventionally, fabrication of such a structure involves a series ofprocess steps by which an “under bump metallization” or UBM layer isintroduced over a die pad opening or on a copper bar redistributionlayer (RDL) previously formed over the die pad openings as shown in FIG.12. A re-passivation (e.g., polyimide (PI)) is then formed, followed bya sputtering step to form the UBM to promote plating. The pillarstructure is then plated on the UBM. In addition to requiring a numberof process steps, this approach places a limit on the width of thepillar (e.g., because of registration tolerances, etc.) which may beunsuitable for some applications. Therefore, according to a particularclass of embodiments, processes for forming copper pillars directly onthe RDL copper without a UBM, or directly on the device pad openings(with or without UBM) are provided.

FIGS. 13(a) and 13(b) show a copper pillar structure formed directly onthe RDL copper which eliminates process steps including formation of aUBM (because the copper pillar will readily plate on the RDL copper).Formation of a passivation may also be avoided although, as shown inFIG. 13(b), a passivation (i.e., the PI layer) may be formed followingpillar formation to inhibit oxidation and any related issues.

FIG. 13(c) shows the copper pillar structure formed directly on the padopening to the top metal layer of the device, but without therepassivation layer required in conventional techniques (see, forexample, PI of FIG. 12), and without the RDL copper shown in otherembodiments. Elimination of the RDL may be feasible, for example, inimplementations in which the Rdson for the device is sufficiently low,e.g., the implementation illustrated in FIG. 5. As will be appreciated,formation of the pillar directly on the pad opening allows exploitationof the entire pad opening for formation of the pillar without anyencroachment of a passivation. In the depicted embodiment, a UBM isshown as it may be necessary to promote adhesion of the pillar structureto the top metal layer of the device. However, embodiments arecontemplated in which a UBM may not be required. As will be understood,a passivation may optionally be applied after pillar formation as shownin FIG. 13(b).

According to a particular process, the structure of FIG. 12 may befabricated according to the following sequence:

-   -   a. Sputter Ti seed layer    -   b. Sputter thin copper seed conductive layer    -   c. Place photo resist    -   d. Plate patterned copper    -   e. Strip photo resist    -   f. Strip seed layers using plated copper as a mask    -   g. Place polyimide (PI)    -   h. Photo expose    -   i. Create openings    -   j. Cure PI    -   k. Sputter Ti seed    -   l. Sputter Cu conductive seed    -   m. Place photoresist    -   n. Plate pattern copper pillar    -   o. Plate solder    -   p. Strip photoresist    -   q. Etch seed

The presence of thick copper in above reduces the requirement for thickcopper on the bottom so one can make copper thinner (3 um instead of 12um) and still get great electrical benefits as the copper is shunting aninner metal layer that is typically not thicker than 1 um.

In an alternate process flow that may be used to fabricate the structureof FIG. 13(a), several steps are eliminated because the final package ismolded. The elimination of these steps (g−1 of the process flowdescribed above) results in the following flow:

-   -   a. Sputter Ti seed layer    -   b. Sputter thin copper seed conductive layer    -   c. Place first photoresist    -   d. Plate patterned copper    -   e. Place second photoresist of dry mask    -   f. Plate copper pillars    -   g. Plate solder    -   h. Strip both photoresists    -   i. Etch single seed

As will be appreciated, this approach eliminates a significant number ofprocessing steps relative to the earlier-described flow, therebyreducing cost. Conductive traces in premolded substrates may be mademore conductive using copper pillars implemented as described in theflows above, or using solder bar structures as described in U.S. patentapplication Ser. No. 12/844,649 for Wafer-Level Chip Scale Package filedJul. 27, 2010, the entire disclosure of which is incorporated herein byreference for all purposes. The copper is in series with traces and thusserves to effectively reduce lateral conductivity of traces. The RDLrouting under the copper pillars may be implemented as described in U.S.patent application Ser. No. 12/343,372 for Flip Chip Power Switch WithUnder Bump Metallization Stack filed Dec. 23, 2008, the entiredisclosure of which is incorporated herein by reference for allpurposes. The on-die connections between interdigitated rows ofdifferent power rails may be implemented as described in U.S. patentapplication Ser. No. 12/343,261 for Conductive Routings in IntegratedCircuits Using Under Bump Metallization filed Dec. 23, 2008, the entiredisclosure of which is incorporated herein by reference for allpurposes.

It should be noted that premolded substrates fabricated in accordancewith various embodiments may be implemented with a wide variety ofconfigurations appropriate for particular applications. For example,some embodiments described herein have relatively unbalancedconfigurations in terms of the conductive traces in the premoldedsubstrate devoted to respective ones of the terminals of a switchingvoltage regulator. See, for example, FIGS. 1-5 in which the conductivetraces corresponding to VSS/GND significantly outnumber those devoted toVin (VDDH). This is due to the fact that these designs are intended forlow duty cycle applications in which the conduction time of theregulator's low-side switch is large compared to that of the high-sideswitch. However, premolded substrates may be fabricated in accordancewith embodiments of the invention for use with more balancedconfigurations in which the duty cycle is much larger. One such floorplan configuration is shown in FIG. 14 in which the respective numbersof VDDH and VSS/GND traces are more balanced. Other examples of morebalanced configurations with which premolded substrates may be employedare described in U.S. patent application Ser. No. 12/344,134 for LeadAssembly for a Flip-Chip Power Switch, referred to and incorporatedherein by reference above. See, for example, FIGS. 9 and 10 of thatapplication. Further examples of more balanced floor plans for whichpremolded substrates may be constructed are provided in U.S. Pat. No.6,278,264 referred to and incorporated herein by reference above. See,for example, FIGS. 3 and 8A-8G of that patent. In addition, furtherembodiments are contemplated in which the conduction time of thehigh-side switch is longer than that of the low-side switch. Therefore,the scope of the invention should not be limited with reference toparticular configurations disclosed herein.

FIG. 15 illustrates yet another floor plan with which a premoldedsubstrate designed in accordance with an embodiment of the invention maybe used which includes alternating rows of conductive traces in thepattern VDDH/VX/GND/VX. The VX conductive traces connect with a full VXplane on one side of the underlying PCB. The VDDH conductive tracesconnect with a VDDH plane on the other side of the PCB shaped as shown.Vias are used to reach internal layers of the PCB. One advantage of theconfiguration depicted in FIG. 15 is zero “current commutation loss.”That is, the same current always flows through the VX traces whether thehigh-side switch or the low-side switch is conducting and does notchange when the conduction is commutated from one to the other. This isto be contrasted with other designs in which current must “redistribute”through the VX traces which, in the presence of stray inductance, causesa delayed turn-on time for some portions of the switches, yieldinghigher resistance and corresponding loss.

While the invention has been particularly shown and described withreference to specific embodiments thereof, it will be understood bythose skilled in the art that changes in the form and details of thedisclosed embodiments may be made without departing from the spirit orscope of the invention. For example, the various structures andtechniques described herein may be compatible with a variety ofpackaging technologies and substrate structures, and the scope ofprotection should therefore not be limited by reference to specifictechnologies or structures. Examples of other technologies andstructures with which various embodiments of the invention may bepracticed include, but are not limited to, ALOX substrate technologyfrom MCL Ltd. of Israel, xLC substrate technology from EoPlexTechnologies, Inc. of Redwood City, Calif., DreamPAK substratetechnology from ASM Pacific Technology Ltd. of the Cayman Islands,Hi-Density Leadframe Array (HLA) technology from United Test andAssembly Center Ltd. (UTAC) of Singapore, and thermal leadless array(TLA) technology from ASAT Ltd. of Dongguan, China (now owned by UTAC'sparent Global A&T Electronics Ltd. of Hong Kong).

Finally, although various advantages, aspects, and objects of thepresent invention have been discussed herein with reference to variousembodiments, it will be understood that the scope of the inventionshould not be limited by reference to such advantages, aspects, andobjects. Rather, the scope of the invention should be determined withreference to the appended claims.

What is claimed is:
 1. A package, comprising: a device including one ormore power devices configured as part of a switching regulator, theswitching regulator having a power node terminal and a switchingterminal; and a premolded interconnect substrate for connecting thedevice to an assembly, the premolded interconnect substrate including aplurality of electrically conductive structures, a first subset of theelectrically conductive structures corresponding to the power nodeterminal, a second subset of the electrically conductive structurescorresponding to the switching terminal; wherein the device is mountedon exposed portions of the electrically conductive structures adjacent afirst surface of the interconnect substrate via conductive bumps therebyconnecting the first subset of the electrically conductive structures tothe power node terminal and the second subset of the electricallyconductive structures to the switching terminal, and wherein exposedportions of the first and second subsets of the electrically conductivestructures at a second surface of the interconnect substrate that isopposite the first surface of the interconnect substrate are configuredfor connection to first and second conductive planes of the assembly,respectively, such that connections between the first subset ofelectrically conductive structures and the first conductive plane aremade along a portion of the second surface of the interconnect substrateproximate a first edge of the interconnect substrate, and connectionsbetween the second subset of electrically conductive structures and thesecond conductive plane are made along a second portion of the secondsurface proximate a second edge of the interconnect substrate opposingthe first edge.
 2. The package of claim 1 wherein the one or more powerdevices comprise two power devices, and wherein the switching regulatorincludes two power node terminals and the switching terminal.
 3. Thepackage of claim 1 wherein at least one of the electrically conductivestructures is enclosed in the interconnect substrate by at least oneother of the electrically conductive structures.
 4. The package of claim1 wherein the device includes control circuitry associated with the oneor more power devices, and wherein some of the electrically conductivestructures correspond to control circuit nodes of the control circuitry.5. The package of claim 1 wherein at least some of the electricallyconductive structures of the interconnect substrate have discretepassive circuit elements connected thereto.
 6. The package of claim 5wherein the discrete passive circuit elements include a plurality ofcapacitors connected to the terminals of the switching regulator.
 7. Thepackage of claim 6 wherein the power node terminal or the switchingterminal has two or more of the plurality of capacitors connectedthereto, the two or more capacitors being mounted on the interconnectsubstrate along more than one edge of the device.
 8. The package ofclaim 6 wherein one or more of the capacitors corresponding to the powernode terminal are mounted along the second edge of the interconnectsubstrate.
 9. The package of claim 5 wherein the electrically conductivestructures to which a first one of the discrete passive elements isconnected are configured for indirect connection to the assembly viainternal routing of the interconnect substrate.
 10. The package of claim5 wherein one or more of the discrete passive circuit elements aremounted on the interconnect substrate between adjacent ones of theconductive bumps.
 11. The package of claim 1 further comprising anunderfill material occupying space between the conductive bumpsconnecting the electrically conductive structures of the interconnectsubstrate to the device.
 12. The package of claim 11 wherein theunderfill material comprises either a dispensed underfill or a moldedunderfill.
 13. The package of claim 11 wherein the underfill material ispart of an encapsulation material at least partially encapsulating thedevice.
 14. The package of claim 1 wherein the device is mounted on theelectrically conductive structures of the interconnect substrate on afirst side of the device, and wherein a second side of the deviceopposing the first side is exposed for heat removal.
 15. The package ofclaim 14 wherein the interconnect substrate includes a thermallyconductive structure, the package further comprising a heat spreaderstructure mounted on the exposed second side of the device and thermallyconnected to the thermally conductive structure of the interconnectsubstrate to promote heat conduction from the device to the thermallyconductive structure.
 16. The package of claim 15 wherein at least aportion of the thermally conductive structure extends through theinterconnect substrate and is configured for connection to the assembly,thereby enabling conduction of the heat from the device to the assembly.17. The package of claim 15 further comprising one or more portions of acarrier frame disposed along one or more edges of the interconnectsubstrate adjacent the device, the heat spreader structure beingthermally connected to the thermally conductive structure of theinterconnect substrate via the portions of the carrier frame.
 18. Thepackage of claim 15 wherein the heat spreader structure comprises aplurality of disconnected or partially connected portions, and/or one ormore apertures.
 19. The package of claim 1 further comprising: a seconddevice; and a second interconnect substrate for connecting the seconddevice to the assembly via the interconnect substrate, the secondinterconnect substrate including a second plurality of electricallyconductive structures; wherein the second device is mounted on exposedportions of the second plurality of electrically conductive structuresvia second conductive bumps, and wherein the second interconnectsubstrate is mounted on the device with at least some of the secondplurality of electrically conductive structures being connected to oneor more of the plurality of electrically conductive structures of theinterconnect substrate via third conductive bumps adjacent an edge ofthe device.